Effect Of Al₄SiC₄ On The Microstructure And Properties Of Recrystallized Silicon Carbide Under Different Atmospheres

Recrystallized silicon carbide is an important high-performance structural ceramic and refractory with excellent thermal stability,excellent mechanical properties at high temperature,high wear resistance,high corrosion resistance,and is the preferred material for national defense,metallurgy,refractory,vehicle engineering,ceramics and other industries.Recrystallized silicon carbide is made of high-purity Si C as raw materials,mixed according to particle gradation,fine particles evaporate at high temperature,condense and sinter at the neck of coarse particles.It is difficult to sinter SiC due to the low diffusion coefficient.In this paper,Al4SiC4 was introduced into the recrystallized SiC system,the effects of different atmospheres,heat treatment temperature and other conditions on the sintering process were studied,and the effect mechanism of recrystallized sintered silicon carbide using Al₄SiC₄ additive was obtained.?1?The Al4SiC4 porous ceramic green body was prepared by the foaming method using Al4Si C4 as raw material and heat-treated under nitrogen atmosphere.The thermal stability of Al4SiC4 in nitrogen was determined by studying the effects of heat treatment temperature and time parameters on the phase composition and micro-morphology of the specimen.The results showed that the Al₄SiC₄ could react with nitrogen,the porous structure could provide increased nitrogen diffusion channels,leading to a decrease in N2 diffusion resistance and an increasing degree of nitridation.The morphology of AlN was influenced by the heat-treatment temperature and time parameters,the Al N and SiC particles had good dispersion and the specimens had homogeneous chemical composition.This method could be used to prepare Al N-SiC porous composite ceramics.?2?The SiC honeycomb ceramic with the addition of Al₄SiC₄ was first heat-treated under nitrogen and then under argon,the effects of in-situ AlN-SiC composite phase on the microstructure and properties of recrystallized SiC were studied.The in-situ generated AlN could form a SiC-AlN solid solution layer on the surface of silicon carbide grain,which could improve the sintering activity of the material and prevent the excessive growth of SiC grains,and had a positive effect on the improvement of mechanical properties of the material.Al N dissolved into SiC grain,reducing the grain boundary energy of SiC and promoting the crystalline transformation from 6H-SiC to 4H-Si C,C could reduce the Si O₂ on the surface of SiC and increase the surface energy,which were helpful for the sintering of the material.?3?The effects of Al₄SiC₄ on the microstructure and properties of recrystallized Si C under argon were studied.The addition of Al4SiC4 to SiC could promote the crystalline transformation from 6H-Si C to 4H-Si C at high temperature.Some SiC particles transformed to hexagonal shape,showing a regular shape of crystal with the increase of Al₄SiC₄.The Al produced by the decomposition of Al₄SiC₄ could dissolve in the SiC lattice,reducing the grain boundary energy of SiC and enhancing the grain boundary diffusion at high temperature.The addition of Al₄SiC₄ could promote the pressureless sintering of Si C ceramics.When 2wt%Al₄Si C₄ was added,the sintered neck developed well,the grain size relatively uniform,and the fracture surface was flat and showed a transgranular fracture mode,which were conducive to the improvement of mechanical properties.